1. Technical Field
The present invention relates to an identification code drawing method, to a substrate, to a display module, and to an electronic apparatus.
2. Related Art
In the related art, in an electro-optical device such as a liquid crystal display device, an organic electroluminescent display device (organic EL display device), a plurality of electro-optical elements are formed on a substrate. In general, on this type of substrate, a unique identification code such as a barcode in which a serial number or the like is encoded for the purpose of quality and product management is drawn. The identification code is read by a dedicated code reader so as to be decoded. However, the substrate on which the identification code is formed not only goes through manufacturing processes of electro-optical elements, but also cleaning/heating processes between the manufacturing processes. Therefore, the substrate is required to be abrasion-resistant, chemically-resistant, and heat-resistant.
Due to such a problem, a method in which heat-resistant adhesive seal on which an identification code is drawn is affixed on a substrate, or a method in which an identification code is directly drawn on a substrate by irradiating a laser beam is proposed. In addition, in JP-A-2003-127537, a method in which water containing an abrasive material is jetted on a substrate so as to mark an identification code on the substrate is proposed. Further, in JP-A-11-77340, a method in which a laser beam is irradiated and a chrome-coated film is transferred onto a substrate so that a mark is formed on the substrate is proposed.
In the above-described methods, there is an advantage in that an identification code which is difficult to be removed from a substrate can be formed. However, a special or an expensive equipment such as a water jet device or a laser sputtering device is needed, which increases a cost and makes it difficult to reduce the size of the equipment. In addition, when an identification code is drawn by irradiation of a laser beam, power consumption increases. Moreover, when water, dust, or the like is adhered on a substrate during a drawing process as in a case in which the water jet device is used, the number of processes increases.
On the other hand, a device which forms the identification code on a glass substrate or the like includes a liquid droplet discharging unit (inkjet device). The liquid droplet discharging unit is a device that discharges liquid droplets containing pigment and the like from a liquid droplet discharging head onto a substrate. Also, the liquid droplet discharging unit is relatively simple and can be made small.
However, depending on liquid used in the liquid droplet discharging unit, the identification code drawn on the substrate abrades to be unclear such that the dedicated code reader cannot read the identification code. Further, as shown in FIG. 10, when liquid droplets 102 are discharged from the liquid droplet head onto a substrate 101 (refer to FIG. 10) having large wettability, there is a case in which the contact angle of the liquid droplet 102 impacted on the substrate 101 becomes small and the liquid droplet 102 spreads over even a non-discharging area where the liquid droplets 102 should not be discharged. As a result, for example, when a two-dimensional code 104 is drawn, the respective dots 103 are connected to one another by spread of liquid droplets as shown in FIG. 11, and accordingly, there is a possibility that the two-dimensional code 104 will not be read by a two-dimensional code reader.
For this reason, in order to form a dot shape, a method may be considered in which a process of discharging a liquid droplet smaller than a dot constituting an identification code onto a dot forming location is performed, a process of drying a substrate is repeatedly performed, and the liquid droplet is impacted onto the dot forming location, thereby making the dot gradually large. However, when the method is employed, the number of processes of drawing the identification code increases, so that the identification code cannot be efficiently formed.